Sweat beads on the paleontologist's reddening forehead as he points to nothing.

More precisely, the jagged buff-colored holes on a jutting slab of mudstone and volcanic ash in this dusty corner of the Mojave Desert show where something used to be. The heart-shaped footprints left by an ancestral camel on a prehistoric lakeside 12 million to 20 million years ago are gone, pinched by a longtime scourge of the desert: fossil thieves.

"More and more, these relics get destroyed because of ignorance or whatever," said Robert Hilburn, a Barstow, Calif., paleontologist and president of the Mojave River Valley Museum there. "Instead, there'll be a heart-shaped piece of rock in a box in somebody's garage."

The prized tracks were fixed in formations that draw paleontologists and geologists from around the world. Minerals from the layers of volcanic ash north of Barstow allow researchers to date the fossils precisely and cross-reference them with other specimens of more uncertain origins. They also offered a singular glimpse into a camel ancestor's pause at an ancient watering hole.

As long as park rangers have been trying to protect the sites, black-market fossil dealers and curious collectors alike have been chipping off chunks of prehistory from Barstow's geologically unique Rainbow Basin Natural Area. Here, the multicolored Barstow Formation is a collision of jumbled angles, with faded red and green rock outcroppings and canyons exposing millions of years of dramatic geologic change, unobscured by vegetation.

Scientists would have to "travel the world over to find all the geologic features you find in this single compressed area," Hilburn said.

California is not as rich in dinosaur bones as Utah, Wyoming or the Dakotas, but it does contain a trove of fossils and artifacts left by prehistoric animals and ancient civilizations. Elephants, rhinoceroses, saber-toothed cats and bear-dog hybrids roamed Southern California millions of years ago, leaving behind bones and tracks. Researchers have also uncovered Native American rock art, arrowheads and cooking pots from as far back as 12,000 years ago.

The market for such items includes both artifacts legitimately unearthed on private lands -- with the owner's permission -- and poached public relics.

Prices for a projectile point from an arrow or spear can run from $50 to $100, said Joan Oxendine, archeologist and cultural resource program manager with the federal Bureau of Land Management in Moreno Valley. Dinosaur skulls cost $10,000 at some gem and mineral shows, and smaller specimens can go for $50 to $200, said Robert Reynolds, a paleontologist and senior cultural resource manager with LSA Associates, a company that helps preserve specimens found during construction projects. Dealers can sell prime mammal fossils for thousands as well.

Thieves routinely outnumber and outmaneuver the few state and federal law enforcement agents responsible for protecting fossils and artifacts on public land.

The BLM has six agents to patrol 3 million acres of the Mojave Desert under its jurisdiction. California state park rangers are responsible for protecting more than 10,000 archeological specimens and countless fossils sprinkled over 1.5 million acres statewide, said Walter Gray, chief of cultural resources for state parks.

State park rangers arrest about 50 "pot hunters" and collectors each year, said Randy Sederquist, chief of the state parks' public safety division.

Experts say the number of violations is impossible to pin down. But when onetime funds were appropriated in 1991 for a full-time cultural site monitor in Joshua Tree, the number of reported archeological violations there jumped from two the previous year to 146. More recently, the number of violators caught has hovered around 10 to 20 annually.

Generally, fewer than 10 such incidents are reported by rangers each year at Death Valley National Park and Mojave National Preserve, said Kathy Clark, staff ranger with the National Park Service's regional office in Denver, which tracks such trends. Nationwide last year, the National Park Service logged 372 violations of laws protecting fossils and archeological relics. Fifty-one cases were prosecuted, spokesman Al Nash said.

Archeological relics such as pots, basketry and masks are in greatest demand, supporting an international underground industry, said Bob Bryson, an archeologist and cultural resources program chief at the Mojave National Preserve.

"It's a huge problem," Bryson said, that "has gone largely unnoticed by the public."

The preserve employs four rangers to cover 1.6 million acres, with two more patrol officers coming, Bryson said.

The desert terrain makes it especially difficult to apprehend thieves. Rangers can rarely sneak up on a fossil poacher, said Roxie Trost, a field manager in the BLM's Barstow office.

"They can see us coming miles away," Trost said. Her office is investigating the stolen camel tracks, which were discovered missing by a geologist last month.

Rangers actually nabbing looters in the act is "pretty rare," said Todd Swain, the lone National Park Service special agent for all of Southern California, who specializes in investigating cultural resource crimes. Investigators rely more on rangers discovering vandalized sites and tips from the public to root out the bandits.

Occasionally, artifacts are picked up by well-meaning hikers and campers who think they are protecting something precious by bringing them to park rangers. Serious souvenir hunters can be as familiar with the nooks and crannies of the vast desert terrain as veteran looters, who are sometimes involved in other illegal activities. Some raiders are out pillaging every weekend for years.

Cultural looting in California is on the rise, said Gray, the state park cultural resource chief, as California's ballooning population spills into formerly isolated areas and all-terrain vehicles allow thieves to motor far into wilderness areas.

And "the power of the Internet has given people . . . the ability to actually reach prospective buyers for objects in an instantaneous manner that didn't exist" before, Gray said.

"Humans by nature are packrats, and there's not a park resource out there . . . that there isn't somebody that isn't just obsessed with collecting to have for their own," Swain said, likening fossil enthusiasts to comic book or Beanie Baby fanatics.

Penalties can be so light -- a fine of a few thousand dollars or several months in jail -- that antiquity thieves can afford to get caught. "It's not like people are going to go to jail for life or they are going to be fined millions of dollars," Swain said.

Fossils and artifacts are "not a renewable resource," Oxendine said.

"The sites fit together in a cultural pattern; if part of that pattern is broken, then that information is lost" forever.

"These are resources that belong to the public," Trost said. "For somebody to go out and remove that, everybody loses."

Paleontologist Robert Hilburn shows where tracks of an early camel were chipped from volcanic ash and mudstone in California's Mojave Desert.The camel track is among the many artifacts in the Mojave Desert. "These relics get destroyed because of ignorance or whatever," Hilburn said.Paleontologist Robert Hilburn visits a part of the Rainbow Basin Natural Area where thieves have removed fossils. Patrolling the vast area is difficult.